Daylily Genetics for Beginners

I have been told that genetics has always been difficult for the non-scientists. I suspect that this might be true for two reasons: 1) it is generally considered a mathematical concept, 2) there may be considerable terminology involved. The following is a simplification (over simplification?) of the genetics of the plants we are most interested in.

We must first realize that all plant characteristics are due to one or more compounds produced by the plant. Each of these compounds is produced as part of a series (pathway) of compounds. Each reaction (one compound produced from another compound) is regulated or caused by a protein (one or more) called an enzyme. The production of all enzymes are caused by the genes. We will assume that each gene (portion of a strand of DNA) causes the production of a particular enzyme. In diploids there are two of each of the chromosomes in each cell. Each of the similar chromosomes typically has the same genes present but sometime the enzymes produced from the function normally, sometimes they do not.

Some definitions of genetic terminology:

Phenotype: General appearance of the flower or plant, such as leaf color, height, width, hardiness, or flower color, size, tepal shape, etc. Some phenotypes are produced by a single pair of genes. Multiple genes or the interaction of genes cause variations in many other characteristics such as height, flower color, size, shape, degree of ruffling, etc.

Genotype: The genetic makeup of the plant producing a particular phenotype or appearance. The genotype is indicated by the actual genes involved not the external characteristic.

Genes: For our purposes, a gene is a portion of DNA on the chromosome, which is responsible for determining the makeup of a protein. Many of these proteins act as enzymes, which may be responsible for determining which chemical reactions occur in the plant. The strands of DNA are at a particular location (locus) in the chromosome. Alleles: Genes located on the same chromosome, in the same position and coding for the same or only slightly different protein/enzyme are considered to be alleles. Dominant: Usually a strand of DNA, which is responsible for the production of an enzyme, which has a noticeable effect (influences phenotype). In daylilies1, yellow appears to be dominate to melon, drab flowers appear to be dominant to clear or not drab.

Recessive: Usually a strand of DNA (gene), which is responsible for the production of a protein (enzyme), which has no noticeable effect (no change in phenotype). We often think of this as a non-functional portion of DNA. In daylilies, likewise, the allele for melon colored flowers would be recessive to the allele for yellow. In other words, the allele for melon is not changing lycopene, a reddish pigment, into ßcarotine to produce a yellow colored flower.

Complete Dominance: A situation where a single strand of DNA (allele) is sufficient to produce all the enzyme needed for the chemical reaction to occur.

0 dominant alleles no color (white)

1 dominant allele most color (dark red)

2 dominant alleles most color (dark red)

3 dominant alleles most color (dark red)

4 dominant alleles most color (dark red)

Incomplete (Partial) Dominance: A situation where a single strand of functional DNA is responsible for the production of an enzyme, but that amount of enzyme is not sufficient to produce the maximum change in the characteristic. In other words – the more dominant genes present the more of an effect will be seen on the phenotype or characteristic:

0 dominant alleles no color (white)

1 dominant allele slight color (light pink)

2 dominant alleles more color (dark pink)

3 dominant alleles much color (light red)

4 dominant alleles most color (dark red)

Homozygous: Referring to a genotype composed of either all dominant or all recessive alleles.

Heterozygous: Referring to a genotype with one or more dominant alleles and one or more recessive alleles.

Enzyme B maybe composed of two kinds of enzymes. These could be of three types:

BB (homozygous, dominant) both copies of the enzyme function normally

Bb (heterozygous) one copy functions normally, one does not function correctly

bb (homozygous, recessive) neither enzyme copy functions correctly (compound B would not be present)

Enzyme C maybe composed of two kinds of enzymes. These could be of three types:

CC both copies of the enzyme function normally

Cc one copy functions normally, one does not function correctly

cc neither enzyme copy functions correctly (compound C would not be present)

1. If lycopene is not produced (enzyme(s) d are not functioning, then Beta Carotene couldn’t be produced either.

2. If lycopene can not be changed to beta-carotene that there will be a build-up of lycopene in the cell. The production of a lot of lycopene in a flower may cause a muddy appearance of the color.

3. The production of beta-carotene in the flower will give it a yellowish cast. Beta-carotene is required for photosynthesis to occur. Photosynthesis is not normally important in the flower itself.

4. A plant with the genetic make-up of yy (non functioning Y enzyme) may decrease the clarity of the flower color in the offspring due to an increase in lycopene storage. Lycopene may be present in higher than normal amounts because it is not being made into carotenoids (beta carotene, xanthophyll and others).

5. A plant with the genetic make-up of YY or Yy (functioning Y enzyme) may increase the clarity of the flower color in the offspring due to a decrease in lycopene storage, but at the same time, increase the yellow pigments. When Lycopene and Carotenoids are not produced (gene dd - non-functional enzyme) the other colors will be sharp and bright. Because of the presence of multiple copies of many of the genes we have yet to totally eliminate carotinoid production. Even our "white" flowers still have some yellow carotinoids present.

Gene Mutations: A change in the DNA of a gene. Gene mutations cause a change in the DNA, which causes 1) a non-functional gene to become functional, 2) a functional gene to change and function for some other purpose or 3) causes an function gene to produce a non-functional protein/enzyme (by far the most common). These gene mutations might be situations where parts of the DNA (bases) are deleted, duplicated, or moved in one way or another.

Chromosomal Mutations: The rearrangement of partial or whole genes, where an entire gene section of a DNA chain is moved from one region of the chromosome to another, or even to another chromosome entirely is called a chromosomal mutation. When the DNA binding site of a regulatory gene moves to a new position, it can then control a new gene. A gene could be moved to a site where it is controlled by a different regulatory gene. These sorts of changes might lead to enzymes being produced at new or different times. This may influence the shapes of flowers (bigger, rounder, ruffled) or to new color combinations and patterns (white flowers, eyes and picotee edges, braided edges, etc.). In general, mutations occur naturally but may be increased by various environmental factors such as certain chemicals, UV light and radiation.

Dominant Mutations: A change in the DNA which produces an enzyme which is functional. Dominant mutations are very rare, but are sometimes very important in introducing brand new characters into the population. If a mutation occurs in the base pairs of a gene, the chances of any base pair being eliminated, replaced, doubled or changed in any way AND produce a working gene/enzyme is slim.

Recessive Mutations: A change in the DNA, which causes the protein ultimately produced from that DNA to no longer function correctly. For example, a gene responsible for a pigment might be changed so that the pigment is no longer produced. Well over ninety-five percent of all mutations are recessive

Hybrid Vigor: Increased heterozygosity (Dd, Yy, Aa,) produces more vigorous plants. Plants, which are inbreed tend to become homozygous (DD, YY, AA, dd, yy, aa) and weaker through the different generations. This is mainly due to the increase in the number of genes which are homozygous and recessive (recessive genes do not function correctly). Hybrid corn is made by crossing two different highly inbreed, nearly homozygous strains. The resulting offspring tend to be much more heterozygous and therefor more vigorous.

Multiple genes: We have assumed during this discussion that each characteristic is determined by a single gene located on homologous chromosomes ( they pair together during meiosis). This may not always be the case. We might assume that many of the characteristics found in daylilies may be determined by more than one gene. Maybe even a dozen genes, possibly located on different chromosomes or on different parts of the same chromosome. If one pair of alleles produces a red colored pigment and another produces a blue pigment, the a purple color would be produced by the flower.

Gene Interactions: Some genes may actually affect the actions of other genes. Some genes may determine whether other genes function at all.

Jumping Genes: Genes will sometime move from one location on a chromsome to another or even from one chromosome to another chromosome. This may happen at any time during development and cell division. This might cause a gene producing a color in the eye to be transfered to a different location where it might cause the gene to produce a pigment influencing throat, or self color. Jumping genes latter in development might cause spotting in the flower.

Ploidy

In many kinds of plants both diploid and polyploid forms occur. The basic or original plant would be diploid with two sets of chromosomes, one set from the male parent and one set from the female parent.

A daylily gamete would normally have 11 chromosomes. Chromosomes are numbered from one to eleven. Any particular nuclear gene is located on one of the eleven chromosomes. For example, a gene responsible for chlorophyll production might be located on chromosome seven (I am not sure what its location actually is and there are probably more than one gene involved). Each chromosome may have thousands of genes, most of which would not be involved in phenotype characteristics which we would easily see. Most produce enzymes involved in metabolism, photosynthesis, and structural products. In diploid plants each cell would have two copies of each gene (22 chromosomes). In tetraploid plants each cell possess four copies of each gene, one on each of the particular chromosomes.

Polyploid plants (with more than two sets of chromosomes) in nature tend to become more abundant as one moves away from the equator. Polyploids tend, in general, to be somewhat hardier, larger more vigorous plants with larger, thicker flowers because they usually have a higher concentration of enzymes and are less likely to be homozygous recessive. One might expect that breeders dealing with polyploid plants would have the upper hand in producing plants with new characteristics, but this is not necessarily true.

See "In favor of diploids"

See "In favor of Tetraploids"

1. Norton, J. 1972. Hemerocallis Journal 26 (3) This information is old and is here merely to be an example.